WERF Benchmark WRRF Configurations

Process flow diagrams for all 18 water resource recovery facility (WRRF) configurations as described in In Zhang et al., 2026 [1]. These configurations were based on the net-zero energy solutions for WRRFs report by the Water Environment Research Foundation (WERF, now a part of the Water Research Foundation, WRF) [2].

Source codes for these configurations can be found in the werf EXPOsan module.

To create any of the system configurations, use the following code, replacing B1 with the desired configuration code (e.g., B2, C3, etc.).

from exposan.werf import create_system

B1 = create_system('B1')
B1.simulate(method='BDF', t_span=(0, 400))
B1.diagram(file='B1', format='html')

Valid configuration codes are: B1, B2, B3, C1, C2, C3, E2, E2P, F1, G1, G2, G3, H1, I1, I2, I3, N1, N2.

Distinguishing features of benchmark WRRF configurations. A WRRF configuration is referred to as a unique combination of a liquid code (a) and a solid code (b) as defined in [2]. Configurations followed by a star (*) are implemented in EXPOsan.

Reading the Diagrams

Every diagram uses the same convention: liquid train across the top with the bioreactor zones in the middle, mixed-liquor recycles (MLR) above the zones, return activated sludge (RAS) below them; solids train across the middle; reject water (centrate + thickener supernatants) returned to the head of the plant along the bottom.

PC Primary clarifier · SC Secondary clarifier · DW Dewatering

GT Gravity thickener · MT Mechanical thickener · MBR Membrane bioreactor

AD Anaerobic digester · AED Aerobic digester

RWW Raw wastewater · ML Mixed liquor

PE Primary effluent · PS Primary sludge

SE Secondary effluent · WAS Waste activated sludge

The configurations are categorized based on their treatment goals:

• rBOD for basic BOD removal (r for readily): B (with primary clarifier) and C (without primary clarifier) series.

• NIT for nitrification: E (aerobic digestion) and F series (anaerobic digestion).

• BNR for biological nutrient removal: G (Johannesburg), H (4-stage Bardenpho+chemicals), I (5-stage Bardenpho), N (5-stage Bardenpho+MBR) series.

B  ·  rBOD with primary clarifier B1 B2 B3

C  ·  rBOD, no primary clarifier C1 C2 C3

E  ·  NIT, aerobic digestion E2 E2P

F  ·  NIT, anaerobic digestion F1

G  ·  BNR, Johannesburg G1 G2 G3

H  ·  BNR, chemical P removal H1

I  ·  BNR, 5-stage Bardenpho I1 I2 I3

N  ·  BNR + MBR N1 N2

B Series: rBOD with Primary Clarifier

Conventional six-zone aerobic activated sludge with short SRT (~2 d) — only BOD removal, nitrifiers wash out. The three B variants differ only in the solids train (AD, AED, or no digestion).

C Series: rBOD without Primary Clarifier

Same six-zone aerobic activated sludge as the B series but without primary clarification — all influent organics enter the bioreactor directly, increasing aeration demand. The three C variants differ only in the solids train (AD, AED, or no digestion).

E Series: NIT with Aerobic Digestion

Longer SRT (~6 d) retains nitrifiers for NH₄⁺ oxidation. E2-P adds primary clarification to the E2 liquid train.

F Series: NIT with Anaerobic Digestion

Compared to E2-P, F1 differs in solids treatment by using anaerobic digestion.

G Series: BNR with Johannesburg Process

BNR configurations with primary clarification. G1–G3 use the Johannesburg step-fed process with external carbon for EBPR;

H Series: BNR with Chemical P Removal

H1 combines chemical phosphorus removal (Fe:sup:3+/Al:sup:3+) with a 4-stage Bardenpho bioreactor and external carbon.

I Series: BNR with 5-stage Bardenpho

Five-stage Bardenpho without primary clarification — raw wastewater provides carbon for denitrification and EBPR without external dosing. The three I variants differ only in the solids train (AD, AED, or no digestion).

N Series: BNR with MBR

Five-stage Bardenpho liquid train with a completely-mixed membrane bioreactor (MBR) replacing the conventional secondary clarifier. N1 includes primary clarification and anaerobic digestion; N2 omits primary clarification and uses aerobic digestion.

[1]

Zhang, X.; Rai, S.; Wang, Z.; Li, Y.; Guest, J. S. An Agile Benchmarking Framework for Wastewater Resource Recovery Technologies. npj Clean Water 2025, 9 (1), 4. https://doi.org/10.1038/s41545-025-00537-4.

[2] (1,2)

Tarallo, S., Shaw, A., Kohl, P. & Eschborn, R. A Guide to Net-Zero Energy Solutions for Water Resource Recovery Facilities. https://iwaponline.com/ebooks/book/293/ (2015).